Image processing apparatus, image processing method, and optical coherence tomography apparatus

ABSTRACT

An image processing apparatus converts an intensity distribution of at least one of a plurality of regions of a tomographic image of an eye by using an amount of conversion which is greater than an amount of conversion used to convert an intensity distribution of another one of the plurality of regions, the tomographic image being obtained by performing tomographic imaging on the eye by using optical interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 15/206,114, filed Jul. 8, 2016, which claims foreign prioritybenefit of Japanese Patent Application No. 2015-140052 filed Jul. 13,2015. The above-named patent applications are hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image processing apparatus and animage processing method for processing a tomographic image obtained byperforming tomographic imaging of an eye by using optical interference.The present invention also relates to an optical coherence tomographyapparatus that performs tomographic imaging of an eye by using opticalinterference.

Description of the Related Art

Optical coherence tomography (OCT) apparatuses that utilizemultiple-wavelength optical interference are being applied to humanorganisms in various fields. For example, the optical coherencetomography apparatuses are used to obtain information about internalorgans with an endoscope or to obtain information about retinas with anophthalmologic apparatus. In outpatient clinics that specialize inretinal care, an optical coherence tomography apparatus applicable toeyes is becoming an indispensable ophthalmologic device. Such an opticalcoherence tomography apparatus irradiates a sample with measuring light,which is low coherent light, and measures backscattered light from thesample by using an interference system. When the optical coherencetomography apparatus is applied to an eye to be examined, ahigh-resolution tomographic image of the eye can be obtained by scanningthe eye with the measurement light. For this reason, optical coherencetomography apparatuses are widely used, for example, for ophthalmicdiagnosis of retinas.

When obtaining a tomographic image of an eye fundus with an opticalcoherence tomography apparatus, it is difficult to obtain a high-qualitytomographic image by scanning the eye with the measurement light oncebecause of the problems of sensitivity and noise. Accordingly, JapanesePatent Laid-Open No. 2015-91552 discloses a technology for increasingthe quality of tomographic images by scanning the same portion of an eyeto be examined a plurality of times to obtain a plurality of tomographicimages, positioning the tomographic images, and then determining theaddition average of the tomographic images.

SUMMARY OF THE INVENTION

An image processing apparatus according to an aspect of the presentinvention includes a tomographic-image acquiring unit configured toacquire a tomographic image of an eye obtained by performing tomographicimaging on the eye by using optical interference; and a processing unitconfigured to convert an intensity distribution of at least one of aplurality of regions of the tomographic image by using an amount ofconversion which is greater than an amount of conversion used to convertan intensity distribution of another one of the plurality of regions.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an optical coherence tomographyapparatus according to an embodiment.

FIG. 2 illustrates an example of an image processing apparatus accordingto the embodiment.

FIG. 3 is a flowchart of an example of an operation of performing anenhancement process after dividing a tomographic image of an eye fundusinto a plurality of regions according to the embodiment.

FIG. 4 illustrates the boundaries between a retina, a vitreous body, anda choroid according to the embodiment.

FIGS. 5A and 5B show examples of histograms of the retina region and thevitreous body and choroid regions, respectively, according to theembodiment.

FIGS. 6A to 6E illustrate examples of enhancement processes for theretina region and the vitreous body and choroid regions, and atomographic image of a retina after an enhancement process according tothe embodiment.

FIGS. 7A to 7C illustrate an example of a method for performing anenhancement process for a specified region based on an operator'sinstruction according to the embodiment.

FIG. 8 is a flowchart of an example of an operation of performing anenhancement process after dividing a tomographic image of an anterioreye portion into a plurality of regions according to the embodiment.

FIGS. 9A to 9E illustrate an example of a method for performing anenhancement process for a specified region based on an operation of apointing device according to the embodiment.

DESCRIPTION OF THE EMBODIMENTS

When generating a tomographic image, an optical coherence tomographyapparatus measures the intensity of interference light by using a sensorand subjects the intensity information of the measured interferencelight to Fourier transformation and logarithmic transformation to obtainoriginal data of a tomographic image. The original data of thetomographic image obtained by Fourier transformation and logarithmictransformation is generally about 32 bits of floating point data or 10or more bits of integer data, and cannot be directly displayed on anordinary display. Therefore, the original data of the tomographic imageneeds to be converted into 8-bit integer data that can be displayed onan ordinary display.

The original data of the tomographic image has a high dynamic rangeincluding very low intensity information and high intensity information.In contrast, 8-bit integer data that can be displayed on an ordinarydisplay has a relatively low dynamic range. Therefore, when the originaldata having a high dynamic range is simply converted into 8-bit integerdata, the contrast of a retina, which is important for diagnosis of aneye fundus, is greatly reduced. Therefore, in a general opticalcoherence tomography apparatus, when the original data is converted into8-bit integer data, a certain amount of low-intensity-side data isdiscarded to ensure appropriate contrast of the retina.

However, when the low-intensity-side information is discarded,information of a vitreous body and a choroid included in the originaldata of the tomographic image will be lost and it will be difficult toobserve the internal structure of the vitreous body and choroid indetail.

In recent years, there has been a need to observe the internal structureof the vitreous body in more detail. However, when the original data ofthe tomographic image is converted into 8-bit integer data so as toensure appropriate contrast of the vitreous body, the contrast of theretina will be reduced, and it will be difficult to observe the internalstructure of the retina in detail.

In light of the above-described circumstances, an embodiment enablesdetailed observation of internal structures of a plurality of regions(for example, retina and vitreous body) on a tomographic image of aneye.

An image processing apparatus according to an embodiment converts anintensity distribution of at least one of a plurality of regions of atomographic image of an eye by using an amount of conversion greaterthan an amount of conversion used to convert an intensity distributionof another one of the plurality of regions, the tomographic image beingobtained by performing tomographic imaging on the eye by using opticalinterference.

Accordingly, the internal structures of a plurality of regions (forexample, retina and vitreous body) can be observed in detail on atomographic image of an eye.

Embodiments of the present invention will now be described.

Structure of Optical Coherence Tomography Apparatus

FIG. 1 illustrates an optical coherence tomography apparatus accordingto an embodiment. An optical interference section 100 includes a lightsource 101, which is a low coherent light source that emits nearinfrared light. Light emitted from the light source 101 propagatesthrough an optical fiber 102 a, and is divided into measurement lightand reference light by a light dividing unit 103. The measurement lightemitted from the light dividing unit 103 enters an optical fiber 102 b,and is guided to a scanning optical system 200. The reference lightemitted from the light dividing unit 103 enters an optical fiber 102 c,and is guided to a reflection mirror 113. The reference light that hasentered the optical fiber 102 c is emitted from an end of the opticalfiber 102 c, passes through a collimating optical system 111 and adispersion compensation optical system 112, and is guided to thereflection mirror 113. The reference light is reflected by thereflection mirror 113, travels along the reverse optical path, andenters the optical fiber 102 c again. The dispersion compensationoptical system 112 compensates for the dispersion of the scanningoptical system 200 and the optical system of the eye E to be examined,which is a measurement target. The reflection mirror 113 can be drivenin an optical axis direction by an optical-path-length controller (notshown), so that the optical path length of the reference light can bechanged relative to the optical path length of the measurement light.The measurement light that has entered the optical fiber 102 b isemitted from an end of the optical fiber 102 b. The light source 101 andthe optical-path-length controller are controlled by a control unit (notshown).

The light source 101 is, for example, a super luminescent diode (SLD),which is a typical low coherent light source, and has a centralwavelength of 855 nm and a wavelength bandwidth of about 100 nm. Thewavelength bandwidth affects the longitudinal resolution, which is theresolution in the optical axis direction, of the tomographic image, andis therefore an important parameter. Although an SLD is selected as thelight source, the type of the light source is not limited as long as lowcoherent light can be emitted. For example, amplified spontaneousemission (ASE) may instead be used. Near infrared light is suitable foruse in the measurement of an eye, and accordingly the central wavelengthis set to 855 nm in the present embodiment. For the purpose ofdiagnosis, it is desirable to enable clear observation of membranesthinner than the junction between photoreceptor inner and outer segments(IS/OS) and the external limiting membrane (ELM). To achieve this, thelongitudinal resolution of the OCT image needs to be 5 μm or less, morepreferably, 3 μm or less. The longitudinal resolution depends on thewavelength bandwidth of the OCT light source. To achieve thelongitudinal resolution of 3 μm or less, the wavelength bandwidth of theOCT light source needs to be about 100 nm or more.

The scanning optical system 200 will now be described. The scanningoptical system 200 is configured to be movable relative to the eye E tobe examined. The scanning optical system 200 is provided with a drivecontroller (not shown) that is capable of driving the scanning opticalsystem 200 in the up-down and left-right directions relative to the eyeaxis of the eye E to be examined. The light emitted from the end of theoptical fiber 102 b is substantially collimated by an optical system202, and is incident on a scanning unit 203. The scanning unit 203includes two galvano-mirrors having rotatable mirror surfaces. Onegalvano-mirror deflects light in a horizontal direction, and the othergalvano-mirror deflects light in a vertical direction. Thus, thescanning unit 203 deflects the incident light under the control of thedrive controller (not shown). In this manner, the scanning unit 203scans light in two directions, which are a main scanning direction alongthe plane of FIG. 1 and a sub-scanning direction perpendicular to theplane of FIG. 1. The light scanned by the scanning unit 203 passesthrough a lens 204 and forms an illumination spot on the eye E to beexamined. The illumination spot moves along the eye E to be examined inresponse to the in-plane deflection by the scanning unit 203. The lightreflected by the eye E to be examined at the illumination spot travelsalong the reverse optical path, enters the optical fiber 102 b, andreturns to the light dividing unit 103.

As described above, the reference light reflected by the reflectionmirror 113 and the measurement light reflected by the eye E to beexamined return to the light dividing unit 103 as returning light, andinterfere with each other so that interference light is generated. Theinterference light passes through an optical fiber 102 d and is emittedtoward a lens 122. Then, the interference light is substantiallycollimated and enters a diffraction grating 123. The diffraction grating123 has a periodic structure, and divides the interference lightincident thereon into interference light components. The interferencelight components are focused on a line sensor 125 by an imaging lens 124capable of changing the focusing state. The line sensor 125 is connectedto an image processing apparatus 300.

Structure of Image Processing Apparatus

FIG. 2 illustrates the image processing apparatus 300. Referring to FIG.2, the image processing apparatus 300 includes a reconstruction unit 301that generates original data of a tomographic image. The opticalcoherence tomography apparatus of the present embodiment is aFourier-domain optical coherence tomography apparatus that generatesoriginal data of a tomographic image of an eye to be examined bysubjecting data output by the line sensor 125 to wave number conversion,Fourier transformation, and logarithmic transformation performed by thereconstruction unit 301. Although a Fourier-domain optical coherencetomography apparatus is used in the present embodiment, a time-domainoptical coherence tomography apparatus may instead be used. Thereconstruction unit 301 is an example of a tomographic-image acquiringunit according to the present embodiment. The reconstruction unit 301may acquire a tomographic image by receiving an interference signalgenerated when the line sensor 125 detects the interference light andreconstructing the tomographic image by using the received interferencesignal. Alternatively, the reconstruction unit 301 may acquire atomographic image by receiving tomographic image data generated by theoptical coherence tomography apparatus.

The image processing apparatus 300 also includes an image analyzer 302that analyzes the generated original data of the tomographic image. Theimage analyzer 302 is capable of analyzing the original data of thetomographic image of the eye to be examined to analyze the structures ofthe eye to be examined included in the original data of the tomographicimage. A region divider 303 is a processor for dividing the originaldata of the tomographic image of the eye to be examined into a pluralityof regions. An enhancement process unit 305 performs contrast andintensity adjustment on the divided regions of the original data of thetomographic image. The enhancement process unit 305 is connected to adisplay 310, which serves as a display unit, so that the tomographicimage that has been subjected to the enhancement process can bedisplayed. The image processing apparatus 300 is connected to a pointingdevice 320. The pointing device 320 is, for example, a mouse including arotating wheel and a button, and is capable of specifying any positionon the display unit 301. In the present embodiment, a mouse is used asthe pointing device. However, other pointing devices such as a joystick,a touch pad, a trackball, a touch panel, and a stylus pen may instead beused.

Thus, the optical coherence tomography apparatus includes the opticalinterference section 100, the scanning optical system 200, and the imageprocessing apparatus 300. At least one or more of the hardwarecomponents of the image processing apparatus 300 may be formed as anindependent device. Alternatively, the components may be provided assoftware that can be installed in one or more computers and thatrealizes the corresponding functions when executed by CPUs (not shown)of the computers. In the present embodiment, it is assumed that thecomponents are realized as software installed in a single computer.

The CPU controls the overall operation of the computer by using programsand data stored in a RAM (not shown) and a ROM (not shown). The functionof each component is realized by controlling the execution of softwarefor each component. The RAM includes an area that temporarily storesprograms and data loaded from a memory medium drive, and a work areaneeded to enable the CPU to perform various processes. The ROM generallystores programs and setting data for the computer. The image processingapparatus 300 may instead be formed as an electric circuit composed ofan image processing board. The optical coherence tomography apparatusand the image processing apparatus 300 may be formed as separateapparatuses that are linked with each other so as to enable wired orwireless communications therebetween. Alternatively, the imageprocessing apparatus 300 may be disposed in and integrated with theoptical coherence tomography apparatus.

Method for Controlling Optical Coherence Tomography Apparatus

A control method for obtaining a tomographic image of an eye to beexamined by using the optical coherence tomography apparatus accordingto the present embodiment will now be determined. First, an operatorrequests a subject to sit in front of the optical coherence tomographyapparatus according to the present embodiment and starts an OCT process.Light emitted from the light source 101 passes through the optical fiber102 a and is divided by the light dividing unit 103 into measurementlight that travels toward the eye to be examined and reference lightthat travels toward the reflection mirror 113. The measurement lightthat travels toward the eye to be examined passes through the opticalfiber 102 b, and is emitted from the end of the optical fiber 102 b.Then, the measurement light is substantially collimated by the opticalsystem 202, and is incident on the scanning unit 203. The scanning unit203 includes galvano-mirrors. The measurement light is deflected by themirrors, passes through the lens 204, and illuminates the eye to beexamined. The light is reflected by the eye to be examined, travelsalong the reverse optical path, and returns to the light dividing unit103. The reference light that travels toward the reflection mirror 113passes through the optical fiber 102 c, and is emitted from the end ofthe optical fiber 102 c. The reference light passes through thecollimating optical system 111 and the dispersion compensation opticalsystem 112, and reaches the reflection mirror 113. The reference lightis reflected by the reflection mirror 113, travels along the reverseoptical path, and returns to the light dividing unit 103. Themeasurement light and the reference light that have returned to thelight dividing unit 103 interfere with each other so that interferencelight is generated. The interference light enters the optical fiber 102d, is substantially collimated by the lens 122, and is incident on thediffraction grating 123. The interference light that has entered thediffraction grating 123 is focused on the line sensor 125 by the imaginglens 124, so that an interference signal for a single point on the eyeto be examined can be obtained.

The interference signal acquired by the line sensor 125 is output to theimage processing apparatus 300. The interference signal output by theline sensor 125 is 12-bit integer data. The reconstruction unit 301subjects the 12-bit integer data to wave number conversion, fast Fouriertransformation (FFT), and logarithmic transformation, thereby generatingoriginal data of a tomographic image in the depth direction at a singlepoint of the eye to be examined. The original data of the tomographicimage generated by the reconstruction unit 301 is 32-bit floating-pointdata. In general, when the interference signal is subjected to FFT,floating point data including decimal numbers is generated. Therefore,when the interference signal is subjected to FFT, the generated data hasa larger number of bits than the 12-bit integer data. The number of bitsof the data obtained by subjecting the interference signal to FFT is notnecessarily 32 as long as it is greater than the number of bits of theinterference signal, and may be, for example, 16 or 64.

After the interference signal for a single point on the eye to beexamined is acquired, the scanning unit 203 drives the galvano-mirrorsso that interference light for another point on the eye to be examinedis generated. The interference light for the other point reaches theline sensor 125, and the reconstruction unit 301 generates original dataof a tomographic image in the depth direction at the other point of theeye to be examined. This control process is repeated to obtain originaldata of a single tomographic image of the eye to be examined. Here, twooperation modes are provided: a first mode in which a certain locationof the eye to be examined is scanned a plurality of times to acquireoriginal data of a tomographic image, and a second mode in which acertain location of the eye to be examined is scanned a plurality oftimes to acquire original data of a plurality of tomographic images. Inthe first mode, the reconstruction unit 301 generates original data of asingle tomographic image. In the second mode, the reconstruction unit301 performs positioning of original data of the tomographic images thathave been acquired, and superposes (determines the average of) theoriginal data of the tomographic images to generate original data of asingle tomographic image.

A procedure for converting an intensity distribution of at least one ofa plurality of regions of a tomographic image of an eye fundus by usingan amount of conversion greater than that used to convert an intensitydistribution of another one of the plurality of regions will now bedescribed.

A procedure for dividing a tomographic image of an eye fundus into aplurality of regions and performing intensity and contrast adjustment oneach of the regions in the optical coherence tomography apparatusaccording to the present embodiment will now be described with referenceto FIG. 3. FIG. 3 is a flowchart of an example of an operation ofperforming an enhancement process after dividing a tomographic image ofan eye fundus into a plurality of regions according to the presentembodiment.

First, in step S101, the reconstruction unit 301 generates original dataof a tomographic image of a retina and outputs the generated originaldata of the tomographic image to the image analyzer 302. The imageanalyzer 302 analyzes the original data of the tomographic image anddetects boundaries between a vitreous body and the retina and betweenthe retina and a choroid on the tomographic image, as illustrated inFIG. 4 (step S102). The detected boundary information is output to theregion divider 303, and the region divider 303 divides the tomographicimage into three regions, which are a vitreous body region Vi, a retinaregion Re, and a choroid region Co, based on the boundary information(step S103).

The region divider 303 determines whether each of the three regionsdivided from each other is the retina region or a region other than theretina region (step S104). Here, it is determined that the retina regionRe is the retina region and that the vitreous body region Vi and thechoroid region Co are regions other than the retina region. The regiondetermined to be the retina region by the region divider 303 issubjected to the process flow starting at step S105. The regionsdetermined as regions other than the retina region by the region divider303 are subjected to the process flow starting at step S108.

In step S105, the enhancement process unit 305 acquires a histogram ofthe retina region Re in the original data of the tomographic image. Asillustrated in FIG. 5A, the acquired histogram of the retina region Rehas a small width Wa, and the brightness at the center position Pa islow. The original data of the tomographic image is 32-bit floating pointdata. When this data is converted into 8-bit integer data that can bedisplayed by the display 310 without changing the shape of thehistogram, an image in which the contrast of the retina region Re isvery low will be obtained, as illustrated in FIG. 6A. To avoid this, theenhancement process unit 305 sets an amount of contrast conversion Ecand an amount of intensity conversion Eb so that the width Wa of thehistogram is converted into a desired width Wr and the center positionPa of the histogram is converted into a desired position Pr (step S106).

$\begin{matrix}{{Ec} = \frac{Wr}{Wa}} & (1) \\{{Eb} = {\Pr - {Pa}}} & (2)\end{matrix}$

In step S107, the enhancement process unit 305 subjects the retinaregion Re, which has been determined as the retina region by the regiondivider 303, to an enhancement process for the original intensity Irrepresented by Equation (3).

Ie=Ir×Ec+Eb  (3)

Here, Ie represents the intensity after the enhancement process, and is8-bit integer data. As a result of this process, as illustrated in FIG.6B, a tomographic image in which the contrast of the retina region Re ishigh is obtained. Therefore, the internal structure of the retina can beobserved in detail. The enhancement process performed on the 32-bit datamay be such that the conversion of the intensity distribution, whichincludes the contrast conversion, and the conversion into 8-bit data areperformed simultaneously, as described above. However, the enhancementprocess for the 32-bit data is not limited to this, and may instead besuch that the conversion of the intensity distribution is performedfirst, and then the conversion into 8-bit data is performed.

In step S108, the enhancement process unit 305 acquires a histogram ofregions other than the retina region in the original data of thetomographic image. As illustrated in FIG. 5B, the acquired histogram ofthe regions other than the retina region has a width Wb smaller thanthat of the histogram of the retina region, and the brightness at thecenter position Pb is lower than that in the histogram of the retinaregion. When this data is converted into 8-bit integer data that can bedisplayed by the display 310 without changing the shape of thehistogram, the vitreous body region Vi and the choroid region Co will beshown as nearly black images, as illustrated in FIG. 6C. To avoid this,the enhancement process unit 305 sets the amount of contrast conversionEc and the amount of intensity conversion Eb so that the width Wb of thehistogram is converted into a desired width Wv and the center positionPb of the histogram is converted into a desired position Pv (step S109).As illustrated in FIG. 5B, the intensity is lower in the vitreous bodyand choroid regions than in the retina region. Therefore, the amount ofcontrast conversion Ec and the amount of intensity conversion Eb for theregions other than the retina region are generally greater than thosefor the retina region.

$\begin{matrix}{{Ec} = \frac{Wv}{Wb}} & (4) \\{{Eb} = {{Pv} - {Pb}}} & (5)\end{matrix}$

In step S110, the enhancement process unit 305 subjects the vitreousbody region Vi and the choroid region Co, which have been determined asthe regions other than the retina region by the region divider 303, toan enhancement process for the original intensity Iv represented byEquation (6).

Ie=Iv×Ec+Eb  (6)

Here, Ie represents the intensity after the enhancement process, and is8-bit integer data. As a result of this process, as illustrated in FIG.6D, a tomographic image in which the contrasts of the vitreous bodyregion Vi and the choroid region Co are high is obtained. Therefore, theinternal structures of the vitreous body and the choroid can be observedin detail. The enhancement process performed on the 32-bit data may besuch that the conversion of the intensity distribution, which includesthe contrast conversion, and the conversion into 8-bit data areperformed simultaneously, as described above. However, the enhancementprocess for the 32-bit data is not limited to this, and may instead besuch that the conversion of the intensity distribution is performedfirst, and then the conversion into 8-bit data is performed.

In step S111, the enhancement process unit 305 combines the image of theretina region Re subjected to the enhancement process in step S107 andthe image of the vitreous body region Vi and the choroid region Cosubjected to the enhancement process in step S110 to generate a single8-bit integer format tomographic image. As illustrated in FIG. 6E, thecontrast of the tomographic image generated in step S111 is high notonly in the retina region Re but also in the vitreous body region Vi andthe choroid region Co, so that the internal structures of the retina,the vitreous body, and the choroid can be observed in detail. Theenhancement process unit 305 outputs the generated tomographic image toa display controller 304, and the display controller 304 displays thetomographic image subjected to the enhancement process on the display310 (step S112).

In this example, the image analyzer 302 detects the boundaries betweenthe retina, the vitreous body, and the choroid in the original data ofthe tomographic image. However, the regions may be subjected todifferent enhancement processes without performing the detection. Forexample, the region divider 303 may divide the original data of thetomographic image into a plurality of regions, and determine whether ornot each region includes any of the retina, vitreous body, or choroid.Based on the result of the determination, it is determined whether ornot each region is the retina region or a region other than the retinaregion. Accordingly, the regions may be subjected to differentenhancement processes.

In the present embodiment, the enhancement processes are performed bydividing the original data of the tomographic image into two groups: theretina region and regions other than the retina region. However, thethree regions, which are the retina region, the vitreous body region,and the choroid region, may instead be individually subjected todifferent enhancement processes. Furthermore, a particularly brightpigment epithelium region or a particularly dark sclera region on theretina may be specified, and the specified regions may be subjected todifferent enhancement processes. Although the original intensity issubjected to linear conversion in the enhancement processes of thepresent embodiment, the enhancement processes are not limited to linearconversion. For example, the original intensity may be converted byusing a conversion function having any curve, such as a gamma curve oran S-curve.

In the present embodiment, a histogram of the retina region and ahistogram the regions other than the retina region are individuallyacquired, and the amount of contrast conversion and the amount ofintensity conversion are determined based on each histogram. However,alternatively, a single histogram may be acquired from the original dataof the tomographic image, and the amount of contrast conversion and theamount of intensity conversion for each region may be determined basedon the single histogram. For example, a histogram of the entire regionof the image is acquired, and the amount of contrast conversion and theamount of intensity conversion for the retina region are determinedbased on the acquired histogram. Next, the amount of contrast conversionand the amount of intensity conversion for the retina region areincreased by using a certain equation, and the increased amounts ofconversion are applied to the regions other than the retina region. Insuch a case, it is only necessary to perform histogram calculation once.

There is no particular limitation regarding the enhancement process unit305 as long as an intensity distribution of at least one of a pluralityof regions is converted by using an amount of conversion greater than anamount of conversion used to convert an intensity distribution ofanother one of the regions. The enhancement process unit 305 may beconfigured to convert the intensity distribution of the region includingat least the vitreous body, which has a relatively low intensitydistribution, so that the region including at least the vitreous body issubjected to an enhancement process. The enhancement process may be anyprocess as long as the intensity distribution of the region isconverted. For example, the enhancement process unit 305 may performonly the contrast conversion among the above-described contrastconversion and intensity conversion. The enhancement process may includegradation conversion of the region instead of the contrast conversion,and the enhancement process unit 305 may convert the intensitydistribution so that the slope of the gradation conversioncharacteristic (for example, gamma), differs between the regions. Asdescribed above, the amounts of conversion, such as the amount by whichthe intensity distribution is expanded and the slope of the gradationconversion characteristic, for the region including at least thevitreous body, which has a relatively low intensity distribution, may begreater than those for the other regions. Accordingly, the internalstructures of the regions having different intensity distributions (forexample, the retina and the vitreous body) can be observed in detail.

In the present embodiment, the retina region and the regions other thanthe retina region are subjected to different enhancement processes.Therefore, there is a possibility that a sudden intensity change occursat the boundaries between the retina region and the regions other thanthe retina region. Such a sudden intensity change is not desirable whenobserving the internal structure of the eye in detail. Therefore, whenthe retina region and the regions other than the retina region aresubjected to different enhancement processes, the enhancement processesmay be performed such that the amount of contrast conversion and theamount of intensity conversion gradually change in the regions aroundthe boundaries.

In the present embodiment, the enhancement process unit 305 subjects theretina region and the regions other than the retina region to differentenhancement processes. However, the enhancement process unit 305 mayperform the same enhancement process for all of the regions. Forexample, as illustrated in FIG. 7A, the display 310 may include avitreous-body emphasizing button for performing an enhancement processfor the vitreous body region and a choroid emphasizing button forperforming an enhancement process for the choroid region. When thesebuttons are not pressed, the entire region of the tomographic image issubjected to the same enhancement process, and the display controller304 displays the image after the enhancement process on the display 310.When the vitreous-body emphasizing button is pressed, as illustrated inFIG. 7B, an enhancement process for strongly emphasizing the vitreousbody region is performed, and the display controller 304 displays theimage after the enhancement process on the display 310. When the choroidemphasizing button is pressed, as illustrated in FIG. 7C, an enhancementprocess for strongly emphasizing the choroid region is performed, andthe display controller 304 displays the image after the enhancementprocess on the display 310. The above-described process allowsphysicians to see an image in which the desired region is emphasizedonly when necessary and observe the internal structure of the desiredportion.

A procedure for converting an intensity distribution of at least one ofa plurality of regions of a tomographic image of an anterior eye portionby using an amount of conversion greater than that used to convert anintensity distribution of another one of the plurality of regions willnow be described.

A procedure for dividing a tomographic image of an anterior eye portioninto a plurality of regions and performing intensity and contrastadjustment on each of the regions in the optical coherence tomographyapparatus according to the present embodiment will now be described withreference to FIG. 8. FIG. 8 is a flowchart of an example of an operationof performing an enhancement process after dividing a tomographic imageof an anterior eye portion into a plurality of regions according to thepresent embodiment.

First, in step S201, the reconstruction unit 301 generates original dataof a tomographic image of an anterior eye portion and outputs thegenerated original data of the tomographic image to the image analyzer302. The image analyzer 302 analyzes the original data of thetomographic image and detects the boundary between the air and a corneasurface and an iridocorneal angle portion on the tomographic image (stepS202). The detected information is output to the region divider 303, andthe region divider 303 divides the tomographic image into three regions,which are an air region Ai, an eye region Ey, and an iridocorneal angleregion An, based on the detected information (step S203). The regiondivider 303 determines whether each of the three regions divided fromeach other is the iridocorneal angle region or a region other than theiridocorneal angle region (step S204). Here, it is determined that theiridocorneal angle region An is the iridocorneal angle region and thatthe air region Ai and the eye region Ey excluding the iridocorneal angleregion are regions other than the iridocorneal angle region. The regiondetermined to be the iridocorneal angle region by the region divider 303is subjected to the process flow starting at step S205. The regionsdetermined as regions other than the iridocorneal angle region by theregion divider 303 are subjected to the process flow starting at stepS208.

In step S205, the enhancement process unit 305 acquires a histogram ofthe regions other than the iridocorneal angle region in the originaldata of the tomographic image. The acquired histogram of the regionsother than the iridocorneal angle region has a small width Wa, and thebrightness at the center position Pa is low. The original data of thetomographic image is 32-bit floating point data. When this data isconverted into 8-bit integer data that can be displayed by the display310 without changing the shape of the histogram, an image in which thecontrast of the eye region Ey excluding the iridocorneal angle region isvery low will be obtained. To avoid this, the enhancement process unit305 sets an amount of contrast conversion Ec and an amount of intensityconversion Eb so that the width Wa of the histogram is converted into adesired width We and the center position Pa of the histogram isconverted into a desired position Pc (step S206).

$\begin{matrix}{{Ec} = \frac{Wc}{Wa}} & (7) \\{{Eb} = {{Pc} - {Pa}}} & (8)\end{matrix}$

In step S207, the enhancement process unit 305 subjects the regions thathave been determined as the regions other than the iridocorneal angleregion by the region divider 303 to an enhancement process for theoriginal intensity Ic represented by Equation (9).

Ie=Ic×Ec+Eb  (9)

Here, Ie represents the intensity after the enhancement process, and is8-bit integer data. As a result of this process, a tomographic image inwhich the contrast of the eye region Ey excluding the iridocorneal angleregion is high is obtained. Therefore, the internal structure of, forexample, the cornea can be observed in detail.

In step S208, the enhancement process unit 305 acquires a histogram ofthe iridocorneal angle region in the original data of the tomographicimage. The acquired histogram of the iridocorneal angle region has awidth Wb smaller than that of the histogram of the regions other thanthe iridocorneal angle region, and the brightness at the center positionPb is lower than that in the histogram of the regions other than theiridocorneal angle region. When this data is converted into 8-bitinteger data that can be displayed by the display 310 without changingthe shape of the histogram, the iridocorneal angle region An will beshown as a nearly black image. To avoid this, the enhancement processunit 305 sets the amount of contrast conversion Ec and the amount ofintensity conversion Eb so that the width Wb of the histogram isconverted into a desired width Wn and the center position Pb of thehistogram is converted into a desired position Pn (step S209). Theintensity is lower in the iridocorneal angle region than in the regionsother than the iridocorneal angle region. Therefore, the amount ofcontrast conversion Ec and the amount of intensity conversion Eb for theiridocorneal angle region are generally greater than those for theregions other than the iridocorneal angle region.

$\begin{matrix}{{Ec} = \frac{Wn}{Wb}} & (10) \\{{Eb} = {{Pn} - {Pb}}} & (11)\end{matrix}$

In step S210, the enhancement process unit 305 subjects the iridocornealangle region An, which has been determined as the iridocorneal angleregion by the region divider 303, to an enhancement process for theoriginal intensity In represented by Equation (12).

Ie=In×Ec+Eb  (12)

Here, Ie represents the intensity after the enhancement process, and is8-bit integer data. As a result of this process, a tomographic image inwhich the contrast of the iridocorneal angle region An is high isobtained. Therefore, the internal structure of the iridocorneal angleportion can be observed in detail. In step S211, the enhancement processunit 305 combines the image of the regions other than the iridocornealangle region subjected to the enhancement process in step S207 and theimage of the iridocorneal angle region An subjected to the enhancementprocess in step S210 to generate a single 8-bit integer formattomographic image. The contrast of the tomographic image generated instep S211 is high not only in the eye region Ey excluding theiridocorneal angle region An but also in the iridocorneal angle regionAn, so that the internal structure of the eye including the iridocornealangle portion can be observed in detail. The enhancement process unit305 outputs the generated tomographic image to the display controller304, and the display controller 304 displays the tomographic imagesubjected to the enhancement process on the display 310 (step S212).

In this example, the image analyzer 302 detects the boundary between theair and the cornea surface and the iridocorneal angle portion in theoriginal data of the tomographic image. However, the regions may besubjected to different enhancement processes without performing thedetection. For example, the region divider 303 may divide the originaldata of the tomographic image into a plurality of regions, and determinewhether or not each region includes any of the air, an eye portion otherthan the iridocorneal-angle portion, or the iridocorneal-angle portion.Based on the result of the determination, it is determined whether ornot each region is the iridocorneal angle region or a region other thanthe iridocorneal angle region. Accordingly, the regions may be subjectedto different enhancement processes.

In the present embodiment, the enhancement process is performed bydividing the original data of the tomographic image into two groups: theiridocorneal angle region and regions other than the iridocorneal angleregion An. However, the three regions, which are the air region, the eyeregion excluding the iridocorneal angle region, and the iridocornealangle region, may instead be individually subjected to differentenhancement processes. Furthermore, a sclera, an anterior chamber, acrystalline lens, a ciliary body, or a vitreous body that can beobserved in the tomographic image may be specified, and the specifiedregions may be subjected to different enhancement processes. Inparticular, although the air region outside the eye appears in thetomographic image of the anterior eye portion, the air region is notused for diagnosis. Therefore, the amount of contrast conversion and theamount of intensity conversion for the air region may be reduced.Alternatively, the enhancement process for the air region may beomitted.

As described above, the tomographic image is divided into a plurality ofregions, and each region is subjected to the corresponding enhancementprocess. Accordingly, the contrast can be increased in each region, andthe internal structures of a plurality of portions can be observed indetail.

A procedure for dividing an original data of a tomographic image into aplurality of regions and adjusting the intensity and contrast for aregion specified on the basis of an operation of a pointing device inthe optical coherence tomography apparatus will now be described.

Enhancement Process of Specified Region in Retina

The reconstruction unit 301 generates original data of a tomographicimage of a retina and outputs the generated original data of thetomographic image to the image analyzer 302. The image analyzer 302analyzes the received original data of the tomographic image and detectsboundaries between a vitreous body and the retina and between the retinaand a choroid on the tomographic image, as illustrated in FIG. 4. Thedetected boundary information is output to the region divider 303, andthe region divider 303 divides the tomographic image into three regions,which are a vitreous body region Vi, a retina region Re, and a choroidregion Co, based on the received boundary information. The enhancementprocess unit 305 subjects the entirety of the original data of thetomographic image to an enhancement process. The processed tomographicimage is displayed on the display 310. As illustrated in FIG. 9A, thedisplay 310 displays not only the tomographic image but also a cursor Ythat indicates a position specified by a pointing device. When adragging operation, which is an operation of moving the pointing devicewhile pressing a button (not shown) on the pointing device, is performedwhile the cursor Y of the pointing device is displayed on thetomographic image, the following operation is performed.

First, the region in which the cursor Y is positioned is selected fromthe three regions. When it is determined that the cursor Y is in thevitreous body region Vi, as illustrated in FIG. 9C, the enhancementprocess unit 305 performs the enhancement process on the vitreous bodyregion Vi on the basis of the operation signal of the pointing device.When it is determined that the cursor Y is in the retina region Re, asillustrated in FIG. 9B, the enhancement process unit 305 performs theenhancement process on the retina region Re on the basis of theoperation signal of the pointing device. When it is determined that thecursor Y is in the choroid region Co, as illustrated in FIG. 9D, theenhancement process unit 305 performs the enhancement process on thechoroid region Co on the basis of the operation signal of the pointingdevice.

In the present embodiment, a mouse is used as the pointing device.However, other pointing devices such as a joystick, a touch pad, atrackball, a touch panel, and a stylus pen may instead be used.Furthermore, the enhancement process may be performed on the basis of anoperation signal generated by any operation of the pointing device otherthan the position specifying operation, such as a wheel-rotatingoperation or a sliding operation, instead of the dragging operation.

In the present embodiment, the region to be enhanced is determined onthe basis of the position of the cursor Y. However, the region to beenhanced can be specified by another method. For example, as illustratedin FIG. 9E, a region selecting button Z may be displayed on the display310, and the region to be subjected to the enhancement process may bedetermined on the basis of the result of selection of the regionselecting button Z.

Enhancement Process of Specified Region in Anterior Eye Portion

First, the reconstruction unit 301 generates original data of atomographic image of an anterior eye portion and outputs the generatedoriginal data of the tomographic image to the image analyzer 302. Theimage analyzer 302 analyzes the original data of the tomographic imageand detects the boundary between the air and a cornea surface and aniridocorneal angle portion on the tomographic image. The detectedinformation is output to the region divider 303, and the region divider303 divides the tomographic image into three regions, which are an airregion Ai, an eye region Ey, and an iridocorneal angle region An, basedon the detected information. The enhancement process unit 305 subjectsthe entirety of the original data of the tomographic image to anenhancement process. The processed tomographic image is displayed on thedisplay 310. The display 310 displays not only the tomographic imagesubjected to the enhancement process but also a cursor Y that indicatesa position specified by a pointing device. When a dragging operation,which is an operation of moving the pointing device while pressing abutton (not shown) on the pointing device, is performed while the cursorY of the pointing device is displayed on the tomographic image, thefollowing operation is performed.

First, the region in which the cursor Y is positioned is selected fromthe three regions. When it is determined that the cursor Y is in the eyeregion Ey, the enhancement process unit 305 performs the enhancementprocess on the eye region Ey on the basis of the operation signal of thepointing device. When it is determined that the cursor Y is in theiridocorneal angle region An, the enhancement process unit 305 performsthe enhancement process on the iridocorneal angle region An on the basisof the operation signal of the pointing device. When it is determinedthat the cursor Y is in the air region Ai, the enhancement process unit305 does not perform the enhancement process on the air region Ai. Thisis because no imaging target is present in the air and the air region Aiis not used for diagnosis.

As described above, by performing the enhancement process on thespecified region of the tomographic image, an image in which only thedesired region is emphasized can be obtained, and the internal structureof the desired portion can be observed in detail.

Other Embodiments

Embodiments of the present invention can also be realized by a computerof a system or apparatus that reads out and executes computer executableinstructions recorded on a storage medium (e.g., non-transitorycomputer-readable storage medium) to perform the functions of one ormore of the above-described embodiment(s) of the present invention, andby a method performed by the computer of the system or apparatus by, forexample, reading out and executing the computer executable instructionsfrom the storage medium to perform the functions of one or more of theabove-described embodiment(s). The computer may comprise one or more ofa central processing unit (CPU), micro processing unit (MPU), or othercircuitry, and may include a network of separate computers or separatecomputer processors. The computer executable instructions may beprovided to the computer, for example, from a network or the storagemedium. The storage medium may include, for example, one or more of ahard disk, a random-access memory (RAM), a read only memory (ROM), astorage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-140052 filed Jul. 13, 2015, which is hereby incorporated byreference herein in its entirety.

1. (canceled)
 2. An ophthalmologic apparatus comprising: a firstdetection unit configured to detect interference light obtained byinterference between returning light from an eye irradiated withmeasurement light and reference light corresponding to the measurementlight; a tomographic image obtaining unit configured to obtain atomographic image of an anterior eye portion of the eye by using thedetected interference light; a region division unit configured to dividethe tomographic image of the anterior eye portion into at least threeregions including an air region, an iridocorneal angle region, and aregion other than the air region and the iridocorneal angle region; anda processing unit configured to convert an intensity distribution of theiridocorneal angle region by using an amount of conversion greater thanan amount of conversion used to convert an intensity distribution of theregion other than the air region and the iridocorneal angle region. 3.The ophthalmologic apparatus according to claim 2, wherein anenhancement process is not performed on the air region.
 4. Theophthalmologic apparatus according to claim 2, further comprising: asecond detection unit configured to detect a boundary between air and acornea surface and the iridocorneal angle region in the tomographicimage of the anterior eye portion by analyzing the tomographic image ofthe anterior eye portion, wherein the region division unit is configuredto divide the tomographic image of the anterior eye portion into the atleast three regions by using a detection result of the second detectionunit.
 5. The ophthalmologic apparatus according to claim 2, wherein theregion other than the air region and the iridocorneal angle region is aninner region of the eye.
 6. The ophthalmologic apparatus according toclaim 2, further comprising: a display control unit configured to causea display unit to display the tomographic image; and a pointing deviceconfigured to specify a position on the displayed tomographic image,wherein the processing unit is configured to perform the enhancementprocess on a region including the specified position by using anoperation signal of the pointing device.
 7. The ophthalmologic apparatusaccording to claim 6, wherein the processing unit is configured toconvert the intensity distribution of the iridocorneal angle region byusing the operation signal of the pointing device in a case where thespecified position is in the iridocorneal angle region of the displayedtomographic image, and the processing unit is configured to convert theintensity distribution of the region other than the air region and theiridocorneal angle region by using the operation signal of the pointingdevice in a case where the specified position is in the region otherthan the air region and the iridocorneal angle region of the displayedtomographic image.
 8. The ophthalmologic apparatus according to claim 2,wherein the region division unit is configured to divide a tomographicimage of an eye fundus of the eye into at least three regions includinga retina region, a vitreous body region, and a choroid region in a casewhere the tomographic image of the eye fundus of the eye is obtained byusing the detected interference light, and wherein the processing unitis configured to convert intensity distributions of the vitreous bodyregion and the choroid region by using an amount of conversion greaterthan an amount of conversion used to convert an intensity distributionof the retina region in a case where the tomographic image of the eyefundus of the eye is obtained by using the detected interference light.9. The ophthalmologic apparatus according to claim 2, wherein thetomographic image obtaining unit is configured to obtain tomographicimage data with resolution higher than display resolution of a displayunit by using the detected interference light, and wherein theprocessing unit is configured to convert tomographic image data obtainedby converting the intensity distributions of the regions intotomographic image data having a number of bits displayable on thedisplay unit.
 10. The ophthalmologic apparatus according to claim 2,wherein the tomographic image obtaining unit is configured to generatetomographic image data having a number of bits larger than eight bits byperforming a predetermined conversion process on intensity informationabout the detected interference light, and wherein the processing unitis configured to convert tomographic image data obtained by convertingan intensity distribution of the generated tomographic image data intotomographic image data in an eight-bit format.
 11. An ophthalmologicapparatus comprising: a first detection unit configured to detectinterference light obtained by interference between returning light froman eye irradiated with measurement light and reference lightcorresponding to the measurement light; a tomographic image obtainingunit configured to obtain a tomographic image of an eye fundus of theeye by using the detected interference light; a second detection unitconfigured to detect at least one layer boundary in the tomographicimage; a region division unit configured to divide the tomographic imageof the eye fundus into at least two regions including a retina regionand a choroid region by using the detected at least one layer boundary;and a processing unit configured to convert an intensity distribution ofthe choroid region by using an amount of conversion greater than anamount of conversion used to convert an intensity distribution of theretina region.
 12. The ophthalmologic apparatus according to claim 11,wherein the processing unit is configured to convert the intensitydistribution of the choroid region in such a manner that the intensitydistribution of the choroid region is expanded, by using an amount ofconversion greater than an amount of conversion used to convert theintensity distribution of the retina region in such a manner that theintensity distribution of the retina region is expanded.
 13. Theophthalmologic apparatus according to claim 11, wherein the processingunit is configured to perform a gradation conversion on the intensitydistribution of the choroid region by using a gradation conversioncharacteristic with a slope greater than a slope of a gradationconversion characteristic used to perform a gradation conversion on theintensity distribution of the retina region.
 14. The ophthalmologicapparatus according to claim 11, wherein the tomographic image obtainingunit is configured to obtain tomographic image data with resolutionhigher than display resolution of a display unit by using the detectedinterference light, and wherein the processing unit is configured toconvert tomographic image data obtained by converting the intensitydistributions of the regions into tomographic image data having a numberof bits displayable on the display unit.
 15. The ophthalmologicapparatus according to claim 11, wherein the tomographic image obtainingunit is configured to generate tomographic image data having a number ofbits larger than eight bits by performing a predetermined conversionprocess on intensity information about the detected interference light,and wherein the processing unit is configured to convert tomographicimage data obtained by converting an intensity distribution of thegenerated tomographic image data into tomographic image data in aneight-bit format.
 16. An ophthalmologic apparatus comprising: a firstdetection unit configured to detect interference light obtained byinterference between returning light from an eye irradiated withmeasurement light and reference light corresponding to the measurementlight; a tomographic image obtaining unit configured to obtaintomographic image data of the eye with resolution higher than displayresolution of a display unit by using the detected interference light;and a processing unit configured to convert an intensity distribution ofthe tomographic image data and convert tomographic image data obtainedby converting the intensity distribution of the tomographic image datainto tomographic image data with the display resolution.
 17. Theophthalmologic apparatus according to claim 16, wherein the tomographicimage obtaining unit is configured to generate tomographic image datahaving a number of bits larger than eight bits by performing apredetermined conversion process on intensity information about thedetected interference light, and wherein the processing unit isconfigured to convert tomographic image data obtained by converting anintensity distribution of the generated tomographic image data intotomographic image data in an eight-bit format.
 18. A control method forcontrolling an ophthalmologic apparatus, comprising: detectinginterference light obtained by interference between returning light froman eye irradiated with measurement light and reference lightcorresponding to the measurement light; obtaining a tomographic image ofan anterior eye portion of the eye by using the detected interferencelight; dividing the tomographic image of the anterior eye portion intoat least three regions including an air region, an iridocorneal angleregion, and a region other than the air region and the iridocornealangle region; and converting an intensity distribution of theiridocorneal angle region by using an amount of conversion greater thanan amount of conversion used to convert an intensity distribution of theregion other than the air region and the iridocorneal angle region. 19.A control method for controlling an ophthalmologic apparatus,comprising: detecting interference light obtained by interferencebetween returning light from an eye irradiated with measurement lightand reference light corresponding to the measurement light; obtaining atomographic image of an eye fundus of the eye by using the detectedinterference light; detecting at least one layer boundary in thetomographic image; dividing the tomographic image of the eye fundus intoat least two regions including a retina region and a choroid region byusing the detected at least one layer boundary; and converting anintensity distribution of the choroid region by using an amount ofconversion greater than an amount of conversion used to convert anintensity distribution of the retina region.
 20. A control method forcontrolling an ophthalmologic apparatus, comprising: detectinginterference light obtained by interference between returning light froman eye irradiated with measurement light and reference lightcorresponding to the measurement light; obtaining tomographic image dataof the eye with resolution higher than display resolution of a displayunit by using the detected interference light; and converting anintensity distribution of the tomographic image data and converttomographic image data obtained by converting the intensity distributionof the tomographic image data into tomographic image data with thedisplay resolution.